1. Field of the Invention
The present invention relates to an electrostatic actuator which is operated by the action of static electricity, and a method of displacement.
2. Description of the Related Art
A conventional actuator and motor are operated mostly by the action of electromagnetic force, and the weights of the permanent magnet and iron core are heavy. Further, the loss of the current flowing in a winding causes enormous heat generation.
On the other hand, an ultrasonic actuator and an ultrasonic motor operated by forces other than electromagnetic force are known. They are driven by the frictional force of a piezoelectric transducer, but their life is too short due to deterioration caused by friction. Besides, for accurate positioning, it is necessary to control the position by using a position sensor such as an encoder. Further, for reducing the size of an ultrasonic actuator, it is necessary to increase the resonance frequency of a piezoelectric element. However, the increased frequency makes it difficult to operate at a low speed.
To solve these problems, several types of electrostatic actuator using electrostatic force have been researched and proposed. Two typical types have been proposed as an actuator capable of generating a relatively large force.
One is the electrostatic actuator disclosed in U.S. Pat. No. 5,448,124 or U.S. Pat. No. 5,541,465. This has a plurality of belt-like electrodes disposed with predetermined intervals in both stator and movable element, and displaces and drives the movable element by the electrostatic force between the stator and movable element by connecting/applying an AC power supply to the electrodes of both stator and movable element.
The other is the contact type electrostatic actuator disclosed in U.S. Pat. No. 5,239,222. This has a stator and a movable element, and applies electric charges from the stator to the movable element comprising a film having a predetermined surface resistivity, and obtains a displacement driving force by generating electrostatic force between the stator and movable element by utilizing a polarization time delay of a dielectric in the movable element.